services/

README

Service packages structure

All service cloud function packages share a consistent structure

Two functions and one type

Initialize function

• Goal
  • Optimize cloud function performance by reducing the invocation latency
• Implementation
  • Is executed once per cloud function instance as a cold start.
  • Cache objects expensive to create, like clients
  • Retreive settings once, like environment variables
  • Cached objects and reteived settings are exposed in one global variable named global

Global type

• A struct to define a global variable carrying cached objects and retreived settings by Initialized function and used by EntryPoint function

EntryPoint function

• Goal
  • Execute operations to be performed each time the cloud function is invoked
• Implementation
  • Is executed on every event triggering the cloud function
  • Uses cached objects and retreived settings prepared by the Initialized function and carried by a global variable of type Global
  • Performs the task a given service is targetted to do that is described before the package key word

Implementation example

How to implement a RAM service package in a Google Cloud function?

go.mod

Replace <vX.Y.Z> in the go.mod file by the RAM version release to be used

module example.com/cloudfunction

go 1.11

require github.com/BrunoReboul/ram <vX.Y.Z>

function.go for a background function triggered by PubSub events

Replace <package_name> by the name of the service package to be used

// Package p contains a background cloud function
package p

import (
    "context"

    "github.com/BrunoReboul/ram/<package_name>"
    "github.com/BrunoReboul/ram/ram"
)

var global <package_name>.Global
var ctx = context.Background()

// EntryPoint is the function to be executed for each cloud function occurence
func EntryPoint(ctxEvent context.Context, PubSubMessage ram.PubSubMessage) error {
    return <package_name>.EntryPoint(ctxEvent, PubSubMessage, &global)
}

func init() {
    <package_name>.Initialize(ctx, &global)
}

function.go for a background function triggered by Google Cloud Storage events

Replace <package_name> by the name of the service package to be used

// Package p contains a background cloud function
package p

import (
    "context"

    "github.com/BrunoReboul/ram/<package_name>"
    "github.com/BrunoReboul/ram/ram"
)

var global <package_name>.Global
var ctx = context.Background()

// EntryPoint is the function to be executed for each cloud function occurence
func EntryPoint(ctxEvent context.Context, gcsEvent ram.GCSEvent) error {
    return <package_name>.EntryPoint(ctxEvent, PubSubMessage, &global)
}

func init() {
    <package_name>.Initialize(ctx, &global)
}

Automatic retrying

Automatic retrying is consistently implemented in RAM service packages as documented in Google Cloud Function best practice Retrying Background Functions

Impact on cloud functions Stackdriver logs:

• Errors entry in log only appears for transient errors.
  • As en error is reported the function is retried.
• Other errors and loged as information to avoid unwanted retries
  • To find errors in such cloud function logs you can use the following Stackdriver logging filter

resource.type="cloud_function"
textPayload:"error"